Brain death occurs when a person has an irreversible, catastrophic brain injury, which causes total cessation of brain function. Some causes of brain death include (but are not limited to): (1) trauma to the brain (ie, severe head injury caused by a motor vehicle crash, gunshot wound, fall or blow to the head), (2) cerebrovascular accident (ie, stroke or rupture of an aneurysm), (3) anoxia (ie, respiratory arrest, drowning), and (4) brain tumor. Ethical standards in the United States mandate that all organ donors must be declared dead before organ donation can proceed. Brain death must therefore constitute a sufficient basis on which to declare a person legally dead. The vast majority of cadaveric organs are procured from donors whose deaths are declared on the basis of brain death. Consequently, cadaveric organ donation is dependent on the ability to reliably determine that a patient is brain dead. Unfortunately, many clinicians remain poorly informed about brain death and how it is defined. The current concept of brain death used in the United States is based on guidelines published in 1981 by the President’s Commission for the Study of Ethical Problems and adopted under the Uniform Determination of Death Act (Table 50-2).8 This act states that death has occurred when there is irreversible cessation of all functions of the brain including the brain stem. Each state government has adopted these guidelines in legislating local criteria for the determination of brain death. The qualifications and number of physicians who must agree on the diagnosis of brain death in order to legally declare a patient brain dead vary considerably among different states. Some states require two separate declaration procedures with a defined time interval between the two examinations. Some states require that two separate physicians make the declaration. In other states a single physician may declare a patient brain dead on the basis of one examination. In no case can the declaring physician take part in the recovery or transplantation of organs from the donor. Most hospitals have established policies within state guidelines for physician qualifications required to make the diagnosis of brain death. Physicians caring for these patients should be aware of local requirements and hospital guidelines in order to facilitate the declaration process and allow termination of care for brain dead patients who will not be organ donors.
TABLE 50-2Defining Brain Death ||Download (.pdf) TABLE 50-2 Defining Brain Death
Guidelines of the
President’s Commission for the Study of
Ethical Problems in Medicine (1981)
Coma with known cause
Documentation of irreversible structural brain injury
Exclusions (preclude diagnosis of coma)
Absence of brain stem function pupillary, corneal, oculovestibular, gag, cough reflexes absent
Apnea (strict definition)
EEG not indicated
Symptoms that support the diagnosis of brain death are the absence of brain stem reflexes, absence of cortical activity, and the demonstration of the irreversibility of this state.9 Therefore, in order to declare brain death there must be a proof of the cause of brain injury; otherwise, the irreversibility requirement cannot be met. Secondly, all reversible causes of coma must be excluded. Causes of reversible coma include hypothermia, hypoxia, hypoglycemia, hyperglycemia, uremia, hepatic failure, Reye’s syndrome, hyponatremia, hypercalcemia, myxedema, adrenal failure, and central nervous system (CNS) depressants. The presence of CNS depressing agents such as narcotics, sedatives, anticonvulsants, anesthetics, and alcohol must be assessed. If any of these agents are present, confirmatory testing is usually required to declare brain death.10 In the brain dead patient, all cranial nerve functions will be absent. The absence of brain stem reflexes must be confirmed by careful neurologic examination. Neuromuscular conduction must be intact in order to allow adequate examination; consequently, the presence of neuromuscular blocking agents must be excluded.
The most definitive finding supporting the diagnosis of brain death is the presence of apnea. The apnea test remains one of the most important parts of the neurologic evaluation of potential organ donors.11 To perform a reliable apnea test the PaCO2 is normalized to 40 mm Hg. The patient is preoxygenated with 100% O2 for at least 5 minutes. The patient is then disconnected from the ventilator and placed on 100% O2 delivered passively to the endotracheal tube via a T-piece at 8–12 L/min. The PaCO2 is allowed to rise to 60 mm Hg, confirmed by a blood gas drawn after approximately 10 minutes. If hemodynamic instability occurs, the patient should be immediately returned to mechanical ventilation and a blood gas should be drawn to assess the PaCO2. If there is any evidence of respiratory activity, the patient is not brain dead and should be immediately returned to the ventilator. If there is no evidence of spontaneous respiratory activity, the PaCO2 has reached 60 mm Hg, and the pH is acidotic, apnea is established and is strongly supportive of brain death.
In many cases confirmatory testing must be performed in addition to a careful neurologic examination in order to firmly establish the diagnosis of brain death. Patients with cervical fractures above the level of C4 may not have intact diaphragmatic function precluding a reliable apnea test. Apnea testing is also unreliable in cases involving overdoses of substances that depress respiratory drive such as alcohol, antiseizure medications, and sedatives. Hemodynamic instability during apnea testing will also preclude the establishment of the diagnosis of brain death on the basis of apnea. In other cases local requirements and or hospital policy may dictate the use of additional confirmatory testing. Confirmatory tests may also be useful in demonstrating a clear etiology for brain death or severe anatomic damage and can decrease the observation period required to establish the diagnosis of brain death.10
Confirmatory tests of brain death include electroencephalogram (EEG) and methods of demonstrating the absence of cerebral blood flow. EEGs are not entirely reliable and are now rarely used for this purpose with the exception of brain death determination in young infants. Demonstration of the absence of cerebral blood flow is the most common confirmatory test currently in use. Methods used to make this determination include cerebral angiography, Doppler ultrasound scanning, and radionuclide cerebral blood flow scanning. The latter two methods are noninvasive, low risk, relatively inexpensive, and are more readily available than cerebral angiography. These tests are highly accurate in verifying the absence of cerebral blood flow and are useful in reducing the time required to establish the diagnosis of brain death. Conversely, an examination that indicates continued cerebral blood flow does not necessarily exclude the diagnosis of brain death. Uncommonly, cerebral blood flow may persist despite brain death due to testing before increasing intracranial pressure completely shuts down flow, skull pliability in infancy or in the presence of decompressing fractures, ventricular shunts, ineffective deep brain flow, reperfusion, brain herniation, jugular reflux, the presence of emissary veins, and pressure injection artifacts.12
Appropriate documentation of brain death is very important in facilitating organ donation for a brain dead patient. The diagnosis of brain death must be documented in writing and it must be unequivocal. The circumstances leading to brain injury, the specific findings of the neurologic examination, and the results of any confirmatory tests should be clearly recorded. Lastly, the date and time of the declaration of brain death must be noted before OPO personnel may obtain the permission of local authorities and the consent of the potential donor’s family. Despite the presence of evidence indicating a person’s desire to be an organ donor, family consent for donation must be obtained. Family refusal is the most common reason that otherwise suitable donors do not become organ donors. If consent for donation is declined, appropriate testing and documentation of brain death is necessary in order to initiate the withdrawal of care.
In some patients with catastrophic brain injury the intracranial pressure (ICP) is maintained and brain death does not occur. However in these patients, the severity of neurologic injury is such the no recovery is expected. Such patients, regardless of the disease process, may be considered for withdrawal of life support because of a hopeless prognosis and for donation after cardiac death (DCD) thereafter. Controlled DCD involves planned withdrawal of ventilatory and organ perfusion support in the face of catastrophic illness. Uncontrolled (currently not practiced in the United States) DCD involves unexpected cardiopulmonary arrest and/or unsuccessful resuscitation, (Maastricht I, II, IV).13 Controlled DCD offers the patient and the family the opportunity to donate organs when criteria for brain death are not met prior to cardiac death. The procurement/transplant team plays no role in whether or when support will be withdrawn.